First MP game underway and as I am a friendly sorta guy I would like to send the odd message to Fafnir my opponent explaining the hopelessness of the Union position and urging him to concede to an unconditional surrender

I am used to the Field of Glory 2 system where a chat box pops up before the turn is sent back but nothing appears here...How do I do that ?
Many thanks in advance for any help (or manual reference will do...I looked but couldn't see it)
Ian